Yes. You can share the resources between Silverlight Modules if you are using Silverlight Toolkit. But there are a lot of problems.. You can't switch the style on the fly os you have to reload the application from code. If you do that, your browser will
be crashed some time.. You won't be able to apply the style to the nested controls. you will need to apply it explicitly. I understand that you are not asking about those problems. So, I would say "Yes! you can share the style and skin between Silverlight
Modules". :)

I think that sharing of resources between modules should be build-in feature of prism. Also there is no app.xaml, so the standart way to add styles and skins inside of module is to make them resource of some control?